fw: use scope_prefix::LOCALHOST in Forwarder

refs #3546

Change-Id: I10a05b642284e7466746cac121d13e7948ca8667
diff --git a/daemon/fw/pit-algorithm.hpp b/daemon/fw/pit-algorithm.hpp
index c5732b8..f901316 100644
--- a/daemon/fw/pit-algorithm.hpp
+++ b/daemon/fw/pit-algorithm.hpp
@@ -33,7 +33,6 @@
  */
 
 namespace nfd {
-namespace fw {
 
 /** \brief contain Name prefix that affects namespace-based scope control
  *  \sa http://redmine.named-data.net/projects/nfd/wiki/ScopeControl
@@ -68,6 +67,8 @@
 
 } // namespace scope_prefix
 
+namespace fw {
+
 /** \brief determine whether forwarding the Interest in \p pitEntry to \p outFace would violate scope
  *  \sa http://redmine.named-data.net/projects/nfd/wiki/ScopeControl
  */